Cathode cooling for electron discharge devices



April 21, 1964 JEWART 3,130,339

CATHODE, COOLING FOR ELECTRON DISCHARGE DEVICES Filed June 2, 1961 INVENTOR A i 'foRNEY Unitcd States Patent 3,130,339 CATHODE COOLING FOR ELECTRON DISCHARGE DEVICES Donmd M. Jewart, Williamsport, Pa., assignor t0 Sylvania Electric Products Inc., a corporation of Delaware Filed June 2, 1951, Ser. No. 114,517 6 Claims. (Cl. 313-40) This invention relates to electron discharge devices employing a thermionic cathode and an anode and more particularly to means for controlling the cathode heating characteristics in such devices.

In many electron tube applications it is necessary to control or regulate the heat imparted to a cathode in order to control the emission therefrom or to prevent damag ng of the cathode due to excessive over-heating. This condition is particularly apt to occur in magnetron type tubes. In such devices, many electrons leave the cathode surface and instead of impinging upon the anode, they actually follow the path of a cardioid to backbomhard the cathode. This bombardment creates undesirable additional cathode heat and secondary emission. In the prior art, the temperature of the cathode, in some magnetrons, was regulated by manual control of a potentiometer or the like external to the magnetron in the heater circuit. Such a control is expensive and difiicult to properly monitor.

Accordingly, it is an object of this invention to automatically cool the cathode of an electron discharge device without varying the cathode heater current when the cathode becomes heated beyond a predetermined temperature.

It is a further object of this invention to provide a thermionic cathode structure wherein cooling of the cathode can be efiected upon reaching a pre-selected temperature.

It is still a further object of the invention to provide a structure wherein cooling of the cathode is effected by reason of its expansion and contact with a heat sink body which forms part of the discharge device.

It is a particular object of this invention to provide a magnetron having an indirectly heated cathode with a cooling member or heat sink adapted to be contacted by the cathode when it is unduly expanded due to overheating to thereby control the temperature of the cathode.

Other objects will become apparent after reading the following specification when taken in conjunction with the accompanying drawing wherein the figure represents in diagrammatic form a section of a magnetron illustrating the elements utilized to effect cooling of the cathode.

The invention is shown as embodied in a magnetron of the cavity-resonator type in which, in conventional fashion, there is provided an anode 19, as of copper, with resonator cavities formed intermediate vanes 12. An output transformer 14 is coupled to the cavities and extends into sleeve 16, which serves to transfer the generated microwave energy to a Waveguide (not shown) through output window 18. The anode is provided with conventional heat radiating fins 29. A pair of pole pieces 24 and 26 are sealed to the anode.

Within the central space of the anode is located a cathode 28 which is associated with a means to effect temperature regulation of the cathode. The cathode 28 is shown partly in section in the drawing and comprises a partially hollow cylinder 30, preferably of molybdenum, extending to a position above pole piece 24 and below pole piece 26. The cathode sleeve is heated by an insulated coiled tungsten heater 32 having an insulated lead portion 34 extending to the exterior of the magnetron through insulating header 48 which is formed to enclose the heater and insulate the central heater lead from ad joining elements. The opposite end of the heater is electrically bonded to cathode 28 as indicated by the joint 29. The open end of the cathode sleeve is mechanically and electrically secured, as by braz ng, to the smaller end of a metallic cone 36. This cone is secured to the pole piece 24 through the intermediary of ring 46, an insulating sleeve 38, and inserts 39 in order to seal the cone to this pole piece. The exterior of cathode sleeve 28 is coated with electron emissive material 40, such as the triple alkaline earth carbonates of barium, calcium and strontium, and is provided with circular fins 42 and 44 to act as shields formed to prevent stray electrons from reaching the pole pieces. The lower surface 41 of the cathode is machined to provide a substantially planar surface for securing good physical contact with heat sink 51 as will be hereafter described. Secured to the metal cone 36 is the metallic ring 46 to which the second lead of heater 35 may be applied in any suitable fashion as by welding.

With the construction described above, it can be seen that the cathode 28 is supported solely at one end by the cone 36. Thus, when the cathode is heated, it is free to expand longitudinally which it will do until the free end surface 41 engages the heat sink or cooling member 5%.

Cathode contact with the cooling member occurs at the end surface 43 of solid cylindrical cooling rod 51, which may be made from molybdenum or tungsten or other high melting point metal. The upper surface 43 is made flat to enable etficient planar contact for heat transfer with the lower surface 41 of cathode 23. The rod has a cylindrical tail section 52 near the upper end of which is located circular flange 54. The heat sink member 5%) slides within and is in heat transfer relationship with a bottomed metallic cooling sleeve 56. This sleeve is circularly brazed at 59 to a flexible diaphragmatic collar 58 of Kovar or the like, which is hermetically sealed to an external electrical insulating supporting sleeve 6'1 This diaphragmatic collar 58 contains a circular fold or crease 61 to facilitate adjustment of heat sink member 5%) as subsequently described. The upper end of external supporting sleeve 60 is suitably sealed to the lower pole piece 26 through inserts S3. Tail section 52 of member 5% slides in contact with the inner wall of cooling sleeve 56. A cup-like adjusting ring 62 of Kovar or other suitable material, having threaded contact with diaphragmatic collar 58, is snugly rotatable on cooling sleeve 56. This sleeve has bearing confinement between the lower edge of diaphragm 58 and the upper surface of the top one of cooling fins 68.

Since adjustment ring 62 is in threaded conjunction with the upper portion of folded diaphragmatic collar 58, rotation of ring 62 causes cooling sleeve 56 to move slightly in and out of external supporting sleeve 60. Inasmuch as sleeve 56 is part of heat sink 50, movement of sleve 56 will change, by degrees of fine adjustment, the space relationship between surfaces 41 and 43 of the cathode 28 and heat sink cooling rod 51 respectively. Thus this space adjustment facilitates the control of cathode temperature to within certain desired limits since the spacing between surfaces 41 and 43 determines when the cooling rod 51 comes in active heat transfer contact with cathode 28. The bottom of cooling sleeve 56 supports a spring 64 formed to react against the bottom of the tail section 5-2 to urge it upwardly. The upward motion of member 50 is limited by the flange 54 engaging a retainer clip 66 on the upper end of the cooling sleeve 56. A plurality of cooling fins 68 are attached to the cooling sleeve to facilitate radiation of heat away from the device.

Upon excessive heating of the cathode during operation of the magnetron due to back electron bombardment, the cathode 28 will elongate longitudinally until surface 41 engages the heat sink or cooling member 50 at surface 43. If excessively hot, the cathode will thrust the member '50 downwardly against the action of spring 64. In normal stable operation, however, mere contact of the cathode against the rod will suflice to conduct suflicient heat'from' the cathode to maintain a prescribed substantially constant cathode temperature. The heat is conducted from cathode 28 into heat sink 50, through sleeve 56 and from radiator fins 68 to the atmosphere.

Thus there is provided in an electron discharge device employing a cathode means for self-regulating the cathode temperature through the contact of a longitudinally expanding cathode with a cooling body. This heat regulation is particularly advantageous since it decreases the limitations in average powercapabilities inherent in the prior art. Hence the functional range of an electron dischange device is usefully extended by automatically and controllably regulating the cathode temperature within desired operational limits. Furthermore, the adjustment feature, whereby the spacing between the cathode and the cooling rod can be desirably regulated, is a means for achieving uniformity between tubes. By this feature, the tube can be pre-set as to operational temperature requirements. In addition, if the situation so warrants, the cathode temperature criteria can be altered during tube operation to achieve optimum results.

Although several embodiments of the invention have been described, it will be apparent to those skilled in the art that variations and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

Having thus described the invention, what is claimed is: 1. In an electron tube including an anode, a thermionic cathode and means for cont-rolling the temperature of the cathode comprising a support for one end of the 7 cathode, the cathode being otherwise unsupported and free to elongate longitudinally, and a cooling member mounted opposite to the unsupported end of the cathode and closely adjacent thereto to be contacted by said cathode on elongation thereof under the influence of heat.

2. In an electron tube having an anode, a thermionic cathode and means for controlling the temperature of the cathode comprising a support for one end of the cathode, the cathode being otherwise unsupported and free to elongate longitudinally, and a cooling member mounted opposite to the unsupported end of the cathode and closely adjacent thereto to be contacted by said cathode on elongation thereof under the influence of heat, said cooling member being in heat transfer relationship with a heat-conductive member extending externally of the tube, and cooling means externally of the tube in contact with said heat conductive member.

3. In an electron tube including an anode, a thermionic cathode and means for controlling the temperature of the cathode comprising a support for one end of the cathode, the cathode being otherwise unsupported and free to elongate longitudinally, a cooling rod mounted opposite to the unsupported end of the cathode and closely adjacent thereto to be contacted by said cathode upon elongation thereof under the influence of heat, a

sleeve extending externally of the tube and means external the tube for cooling said sleeve, said cooling rod 4 being formed for slidable heat transfer engagement with said sleeve.

4. In an electron tube including an anode, a thermionic cathode and means for controlling the temperature of the cathode comprising a support for one end of the cathode, the cathode being otherwise unsupported and free to elongate longitudinally, a cooling rod mounted opposite to the unsupported end of the cathode and closely adjacent thereto to be contacted by said cathode upon elongation thereof under the influence of heat, said cooling rod extending into a bottomed cooling sleeve, said cooling rod being formed for slidable heat transfer engagement with said cooling sleeve, a spring between the bottom of said cooling sleeve and the rod to urge the rod upwardly toward the cathode, cooperating means on the rod and sleeve to limit the upward movement of the rod, and cooling fins external of the tube connected to said sleeve.

5. In an electron tube including an anode, a thermionic cathode and means for controlling the temperature of the cathode comprising a support for one end of the cathode, the cathode being otherwise unsupported and free to elongate longitudinally, a cooling rod mounted opposite to the unsupported end of the cathode and closely adjacent thereto to be contacted by said cathode upon elongation thereof under the influence of heat, said cooling rod extending into a bottomed cooling sleeve, said means for heating the cathode, a fixed support at one end of said tube to which an end portion of said cathode is secured, the cathode being otherwise unsupported, a second support at the other end of the tube, a cooling device including a rod supported by the second support, said rod terminating close to the unsupported end of the cathode to abstract heat from the cathode on thermal extension thereof, said cooling device further including a heat conductive sleeve Within which the rod slides, spring means reacting between the heat conductive sleeve and rod to urge the rod toward the free end of the cathode, and interacting means on the rod and heat conductive sleeve to limit the motion of the rod toward the cathode, said heat conductive sleeve being longitudinally adjustable in said second support toward and from the cathode sleeve.

Hanson et va1. Feb. 1, 1949 Thomson et al Sept. 11, 1951 

6. A MAGNETRON TUBE INCLUDING A PAIR OF OPPOSED POLE PIECES, AN ANODE THEREBETWEEN, A CATHODE EXTENDING CENTRALLY THROUGH THE ANODE AND SPACED THEREFROM AND MEANS FOR HEATING THE CATHODE, A FIXED SUPPORT AT ONE END OF SAID TUBE TO WHICH AN END PORTION OF SAID CATHODE IS SECURED, THE CATHODE BEING OTHERWISE UNSUPPORTED, A SECOND SUPPORT AT THE OTHER END OF THE TUBE, A COOLING DEVICE INCLUDING A ROD SUPPORTED BY THE SECOND SUPPORT, SAID ROD TERMINATING CLOSE TO THE UNSUPPORTED END OF THE CATHODE TO ABSTRACT HEAT FROM THE CATHODE ON THERMAL EXTENSION THEREOF, SAID COOLING DEVICE FURTHER INCLUDING A HEAT CONDUCTIVE SLEEVE WITHIN WHICH THE ROD SLIDES, SPRING MEANS REACTING BETWEEN THE HEAT CONDUCTIVE SLEEVE AND ROD TO URGE THE ROD TOWARD THE FREE END OF THE CATHODE, AND INTERACTING MEANS ON THE ROD AND HEAT CONDUCTIVE SLEEVE TO LIMIT THE MOTION OF THE ROD TOWARD THE CATHODE, SAID HEAT CONDUCTIVE SLEEVE BEING LONGITUDINALLY ADJUSTABLE IN SAID SECOND SUPPORT TOWARD AND FROM THE CATHODE SLEEVE. 